Airworthiness Directives; The Boeing Company Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

Airworthiness Directives; The Boeing Company Airplanes

Federal Aviation Administration (FAA), DOT.

Notice of proposed rulemaking (NPRM).

The FAA proposes to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 737 -300, -400, and -500 series airplanes. This proposed AD was prompted by reports of nuisance stick shaker activation while accelerating to cruise speed at the top of a climb due to frozen angle of airflow (AOA) sensor vanes. This proposed AD would require installing new external case heaters (ECHs) on the left and right AOA sensors, performing repetitive functional tests and applicable corrective actions, and accomplishing applicable concurrent actions. The FAA is proposing this AD to address the unsafe condition on these products.

The FAA must receive comments on this proposed AD by October 2, 2026.

You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods: Federal eRulemaking Portal: Go to regulations.gov. Follow the instructions for submitting comments. Fax: 202-493-2251. Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590. Hand Delivery: Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. AD Docket: You may examine the AD docket at regulations.gov under Docket No. FAA-2026-7237; or in person at Docket Operations between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this NPRM, any comments received, and other information. The street address for Docket Operations is listed above. Material Incorporated by Reference: For Boeing material identified in this proposed AD, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone 562-797-1717; website myboeingfleet.com. You may view this material at the FAA, Airworthiness Products Section, Operational Safety Branch, 2200 South 216th St., Des Moines, WA. For information on the availability of this material at the FAA, call 206-231-3195. It is also available at regulations.gov under Docket No. FAA-2026-7237.

Michael Closson, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206- 231-3973; email: [email protected].

Comments Invited

The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments using a method listed under the ADDRESSES section. Include "Docket No. FAA-2026-7237; Project Identifier AD-2025-01425-T" at the beginning of your comments. The most helpful comments reference a specific portion of the proposal, explain the reason for any recommended change, and include supporting data. The FAA will consider all comments received by the closing date and may amend this proposal because of those comments.

Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in 14 CFR 11.35, the FAA will post all comments received, without change, to regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this NPRM.

Confidential Business Information

CBI is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to this NPRM contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this NPRM, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as "PROPIN." The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this NPRM. Submissions containing CBI should be sent to Michael Closson, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3973; email: [email protected]. Any commentary that the FAA receives that is not specifically designated as CBI will be placed in the public docket for this rulemaking.

Background

The FAA has received reports of nuisance stick shaker activation on Model MD-90 airplanes while the airplane was accelerating to cruise speed at the top of a climb. A review of recorded flight data and weather reports indicated that the nuisance stick shaker activation was caused by AOA sensor vanes that were frozen and malfunctioned due to insufficient heat in certain AOA sensors that prevent ice build-up in the vane pivot. Heavy moisture conditions on the ground can lead to water entering the AOA vane pivot and freezing prior to or during flight. The manufacturer has determined that the potential for vane pivot freezing exists on AOA sensor part numbers used on certain Model 737, -300, -400, and -500 series airplanes. This condition, if not addressed, could lead to failure of the stall warning system and result in a loss of continued safe flight and landing.

FAA's Determination

The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop on other products of the same type design.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 737-30A1081 RB, Revision 1, dated April 30, 2026. This material specifies procedures for installing new ECHs on the left and right AOA sensors, performing repetitive functional tests and applicable corrective actions (e.g., includes troubleshooting and replacing the ECH), and accomplishing applicable concurrent actions. Concurrent actions include installing a junction box, installing air data probe heat automation wire provisions, replacing insulation blankets with new flame retardant material, modifying circuit breaker panels to activate the automated probe heat system, and modifying or replacing the identification label on certain AOA sensors, as applicable. Concurrent actions also include, if any crack is found, contacting Boeing for repair instructions and doing the repair. This material is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section.

Proposed AD Requirements in This NPRM

This proposed AD would require accomplishing the actions specified in the material already described, except for any differences identified as exceptions in the regulatory text of this proposed AD. For information on the procedures and compliance times, see this material at regulations.gov under Docket No. FAA-2026-7237.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 133 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD:

Estimated Costs

Cost on U.S. Action Labor cost Parts cost Cost per product operators

Installation..................... 13 work-hours x $85 $1,020 $2,125.............. $282,625. per hour = $1,105. Functional test.................. 1 work-hours x $85 0 $85 per test cycle.. $11,305 per test per hour = $85 per cycle. test cycle. Concurrent actions............... Up to 888 work-hours 34,403 Up to $109,883...... Up to $14,614,439. x $85 per hour = $75,480.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority. The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: General requirements. Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.